Light Regulation of Leaf Mitochondrial Pyruvate Dehydrogenase Complex

Abstract

Light-dependent inactivation of mitochondrial pyruvate dehydrogenase complex (mtPDC) in pea (Pisum sativum L.) leaves was further characterized, and this phenomenon was extended to several monocot and dicot species. The light-dependent inactivation of mtPDC in vivo was rapidly reversed in the dark, even after prolonged illumination. The mtPDC can be efficiently cycled through the inactivated-reactivated status by rapid light-dark cycling. Light-dependent inactivation of mtPDC was shown to be suppressed by inhibitors of photorespiratory carbon metabolism, including 2-pyridylhydroxymethane sulfonate, isonicotinic acid hydrazide, and aminoacetonitrile, and by an inhibitor of photosynthesis, 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Glycine fed to pea leaf strips in the dark yielded partially inactivated leaf mtPDC, and this inactivation was blocked by inhibitors of glycine oxidation. It is concluded that the photorespiratory glycine to serine conversion that occurs in C3 leaf mitochondria can provide the NADH to drive oxidative phosphorylation and subsequent inactivation of mtPDC. Glycine oxidation also produces ammonium ion, which has been shown to enhance the inactivation of mtPDC in vitro by stimulating the pyruvate dehydrogenase kinase that catalyzes the phosphorylation (inactivation) of the mtPDC. Thus, light-dependent, photorespiration-stimulated inactivation of the mtPDC can regulate carbon entry into the Krebs cycle during C3 photosynthesis.The mtPDC2 links glycolytic carbon metabolism with the Krebs cycle by catalyzing the oxidative decarboxylation of pyruvate to acetyl-CoA. Pyruvate provides the primary substrate for the Krebs cycle, which, in turn, provides the reducing equivalents for ATP production by oxidative phosphorylation. for regulation of the mitochondrial complex through product feedback by NADH and acetyl-CoA (23) and inactivationreactivation by reversible phosphorylation (26,27). Plants are unique in having an additional isoform of PDC in their plastids (10, 11) that is also quite sensitive to product feedback regulation but does not undergo regulation by reversible phosphorylation (10,27). In vitro studies of the PDC kinase have also shown that the phosphorylation-inactivation reaction is stimulated by micromolar NH4+ (29) and is inhibited by pyruvate, the substrate for the PDC (26,30). In situ studies with purified pea leaf mitochondria have shown that the PDC phosphorylation status is increased when the mitochondria are oxidizing substrates other than pyruvate (6), in particular, glycine, an intermediate of the photorespiratory carbon oxidation pathway.The controversy of whether or not mitochondrial respiration is occurring during photosynthesis has been long standing (16), and recent reports by Kromer and colleagues (20, 21) working with barley (Hordeum vulgare) leaf protoplasts provide convincing evidence that mitochondrial ATP production is required for optimal photosynthesis. However, Budde and Randall (7,8) recently reported that the pea leaf mtPDC is primarily in an inactivate...

Distribution of Pyruvate Dehydrogenase Complex Activities between Chloroplasts and Mitochondria from Leaves of Different Species

“…Vol. 106,1994 occurring (Browse et al, 1981), the mtPDC of pea has been shown to be inactivated (Budde and Randall, 1990;Gemel and Randall, 1992). This might indicate that the illuminated chloroplast must be at least partially self-providing with respect to substrate for cpPDC, whereas in darkness acetyl-COA used in the stroma is produced to a greater extent in the mitochondria.…”

“…The phosphorylation state of mtPDC is determined by the combined action of PDC kinase and phosphatase. It has been proposed that the mtPDC in vivo is less active in light compared to darkness (Budde and Randall, 1990; Gemel and Randall, 1992). This inhibition could be due to ammonium produced in the mitochondrial matrix by the Gly decarboxylase complex active in photorespiratory metabolism.…”

“…This inhibition could be due to ammonium produced in the mitochondrial matrix by the Gly decarboxylase complex active in photorespiratory metabolism. Inactivation of mtPDC has been shown to be depressed when photorespiration was blocked (Gemel and Randall, 1992), and ammonium ions have been shown to be potential activators of mtPDC kinase (Schuller and Randall, 1989). The stromal cpPDC produces acetyl-building blocks for fatty acid, isoprenoid, and amino acid biosynthesis within the chloroplast.…”

A Tale of Two Sugars: Trehalose 6-Phosphate and Sucrose

“…Potentially this could be brought about by Tre6P-triggered changes in the phosphorylation status of the mPDH. This enzyme is usually inactivated by phosphorylation during the day (Budde and Randall, 1990;Gemel and Randall, 1992;Tovar-Méndez et al, 2003), restricting the provision of acetyl-CoA for citrate synthesis, which mainly occurs during the night (Gauthier et al, 2010;Tcherkez et al, 2012;Ishihara et al, 2015).…”

Monovalent Cation Activation of Plant Pyruvate Dehydrogenase Kinase

“…Thus, w e conclude that the monovalent cations do not stimulate the kinase by overcoming ADP inhibition or by increasing the K,(ADP). We also propose that the NH4+ produced during photorespiratory glycine oxidation in the mitochondria will stimulate the light-dependent inactivation of PDC as reported by Budde a n d Randall (1990) a n d Gemel a n d Randall (1992).…”